A major cause for the spread of AIDS in the general population is the presence of IV drug users who share and reuse hypodermic syringes to inject drugs. Infection can also be spread from AIDS patients in hospitals and medical facilities through accidental needle sticks with needles used on infected patients. Used syringes with extended needles present a risk not only to medical personnel but also to sanitation employees and others in the disposal chain.
There are a number of syringes of different designs which have needles which will retract at the end of the injection cycle. Most of these have never reached the market because of various deficiencies. Prime among the usual deficiencies of the prior art are problems of complexity, reliability and cost. Medical syringes are produced and used by the millions every day. Cost is a significant factor both in manufacture of the parts and assembly of the device.
A principal problem with the prior art devices is the fact that in order to retract the needle, some part or parts must flex and bend, break or a diaphragm must be ruptured at a particular stage in the operation. A number of these prior art references are briefly discussed in my co-pending patent application Ser. No. 08/125,292, filed Sep. 21, 1993, which is incorporated by reference. The problems of complexity, reliability and cost are intertwined since things that are more complex generally have a higher failure rate and cost than do simpler devices. This is particularly true in the miniature one cc syringes which are the most commonly manufactured and used syringes. It is far more difficult to miniaturize complex retraction mechanisms and still have the parts function effectively and reliably.
It would be highly desirable to produce a medical device, in the form of a syringe, which meets the requirements mentioned. Suitable syringes should at least 1) maintain the same capacity to hold fluids and offer accurate incremental measurement of fluid as compared with standard syringes; 2) permit one-handed use so that the other hand of the health care worker is free to assist in holding the patient; 3) retract fully after use and thereby eliminate needle sticks because of mistaken belief that retraction has occurred when, in fact, it hasn't; 4) indicate prior use; 5) be extremely reliable, even over a wide range of temperature; 6) be easily assembled for mass production; 7) be manufactured at extremely low cost; and 8) operate reliably under a variety of circumstances. The invention disclosed herein meets these requirements and more.